Systems for inducing fluid flow to stimulate tissue growth

ABSTRACT

Provided are apparatuses, systems, and methods for treating tissue at a tissue site in a mammal that includes a scaffold adapted to be disposed adjacent to the tissue site and to be fluidly coupled to a blood vessel of the mammal for receiving blood therefrom. Additionally, a scaffold is provided that includes a charged surface comprising a streaming potential.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/648,453, filed Dec. 29, 2009 now U.S. Pat. No. 8,197,551 entitled“Systems for Inducing Fluid Flow to Stimulate Tissue Growth”, whichclaims the benefit, under 35 USC §119(e), of the filing of U.S.Provisional Provisional Application No. 61/238,770, filed Sep. 1, 2009,U.S. Provisional Application No. 61/142,053, filed Dec. 31, 2008, andU.S. Provisional Application No. 61/142,065, filed Dec. 31, 2009, all ofwhich are hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present application relates generally to tissue engineering and inparticular to scaffolds, systems, and methods suitable for use intreatment of tissue.

2. Description of Related Art

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but application of reduced pressure has beenparticularly successful in treating wounds. This treatment (frequentlyreferred to in the medical community as “negative pressure woundtherapy,” “reduced pressure therapy,” or “vacuum therapy”) provides anumber of benefits, including faster healing and increased formation ofgranulation tissue. Typically, reduced pressure has been applied totissue through a porous pad or other manifolding device. The porous padcontains pores that are capable of distributing reduced pressure to thetissue and channeling fluids that are drawn from the tissue. The porouspad often is incorporated into a dressing having other components thatfacilitate treatment. A scaffold can also be placed into a defect tosupport tissue growth into the defect. The scaffold is usuallybioabsorbable, leaving new tissue in its place.

Scaffolds for reduced pressure treatment are described in, for example,WO08/091521, WO07/092397, WO07/196590, WO07/106594. The adequacy ofcurrent scaffolds for reduced pressure treatment can be evaluated inlight of current knowledge of wound healing. Injury to body tissuesresults in a wound healing response with sequential stages of healingthat include hemostasis (seconds to hours), inflammation (hours todays), repair (days to weeks), and remodeling (weeks to months). A highlevel of homology exists across most tissue types with regard to theearly phases of the wound healing process. However, the stages ofhealing for various tissues begin to diverge as time passes, with theinvolvement of different types of growth factors, cytokines, and cells.The later stages of the wound healing response are dependent upon theprevious stages, with increasing complexity in the temporal patterningof and interrelationships between each component of the response.

Strategies to facilitate normal repair, regeneration, and restoration offunction for damaged tissues have focused on methods to support andaugment particular steps within this healing response, especially thelatter aspects of it. To this end, growth factors, cytokines,extracellular matrix (ECM) analogs, exogenous cells, and variousscaffolding technologies have been applied alone or in combination withone another. Although some level of success has been achieved using thisapproach, several key challenges remain. One main challenge is that thetiming and coordinated influence of each cytokine and growth factorwithin the wound healing response complicate the ability to addindividual exogenous factors at the proper time and in the correctcoordination pattern. The introduction of exogenous cells also facesadditional complications due to their potential immunogenicity as wellas difficulties in maintaining cell viability.

Synthetic and biologic scaffolds have been utilized to providethree-dimensional frameworks for augmenting endogenous cell attachment,migration, and colonization. To date, nearly all scaffolds have beendesigned with the idea that they can be made to work with in situbiology. Traditional scaffolding technologies, however, rely on thepassive influx of endogenous proteins, cytokines, growth factors, andcells into the interstitium of the porous scaffold. As such, thecolonization of endogenous cells into the scaffold is limited by thedistance away from vascular elements, which provide nutrient supportwithin a diffusion limit of the scaffold, regardless of tissue type. Inaddition, the scaffolds can elicit an immunogenic or foreign bodyresponse that leads to an elongated repair process and formation of afibrous capsule around the implant. Taken together, these complicationscan all lead to less than functional tissue regeneration at the injurysite.

It would therefore be advantageous to provide additional systems tofurther direct healing and tissue growth. The present invention providessuch systems.

SUMMARY

The scaffolds, systems, and methods of the illustrative embodimentsdescribed herein are designed to provide active guidance of tissueregeneration through an implanted scaffold. In one embodiment, a systemfor treating tissue at a tissue site in a mammal is provided thatincludes a scaffold adapted to be disposed adjacent to the tissue siteand to be fluidly coupled to a blood vessel of the mammal for receivingblood therefrom, and a valve adapted to be fluidly coupled to the bloodvessel and controllable between an open position and a closed positionfor regulating the flow of the blood from the blood vessel to thescaffold. In this system, the valve allows the blood to flow from theblood vessel into the scaffold when in the open position and preventsthe blood from flowing into the scaffold when in the closed position.

In another embodiment, a system for facilitating growth of tissue at atissue site of a patient is provided that includes a scaffold adaptablefor implantation at the tissue site for providing a structural matrixfor the growth of the tissue and further adaptable for being fluidlycoupled to a blood vessel of the patient, a valve controllable betweenan open position and a closed position for regulating the flow of bloodfrom the blood vessel to the scaffold, and a controller operably coupledto the valve to vary the valve between the open position and the closedposition. In this system, the valve allows the blood to flow from theblood vessel into the scaffold when in the open position and preventsthe blood from flowing into the scaffold when in the closed position.

In an additional embodiment, a scaffold suitable for implantation into abone defect or fracture is provided that includes a charged surfacecomprising a streaming potential, wherein, when implanted in a bonedefect, electrolytic fluids comprising blood or interstitial fluids fromtissue adjacent to the scaffold are drawn across the charged surface ofthe scaffold by the streaming potential.

In a further embodiment, a method of treating a bone having a defect orfracture is provided that includes implanting the above scaffold intothe defect or fracture. Also, a method of modifying a scaffold that issuitable for implantation into a bone defect or fracture is providedthat includes inducing a charge onto a surface of the scaffold.

Other objects, features, and advantages of the illustrative embodimentswill become apparent with reference to the drawings and detaileddescription that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustrative embodiment of a reduced pressure therapysystem, with a portion shown in cross-section, for treating a tissuesite using a scaffold;

FIG. 1A is a cross-section view of the system of FIG. 1 taken on theline 1A-1A;

FIG. 2 shows an illustrative embodiment of a portion of a reducedpressure therapy system, with a portion shown in cross-section, fortreating a tissue site using a scaffold; and

FIG. 3 is a cross-sectional view of a scaffold at a tissue site inaccordance with an illustrative embodiment.

DETAILED DESCRIPTION

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention, and it is understood thatother embodiments may be utilized and that logical structural,mechanical, electrical, and chemical changes may be made withoutdeparting from the spirit or scope of the invention. To avoid detail notnecessary to enable those skilled in the art to practice the embodimentsdescribed herein, the description may omit certain information known tothose skilled in the art. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of theillustrative embodiments are defined only by the appended claims.

Referring to FIGS. 1 and 1A, a reduced pressure therapy system 100 forapplying reduced pressure and facilitating the growth of tissue at atissue site 102 in the body of a patient such as, for example, in a limb103 of the patient, is shown. The reduced pressure therapy system 100comprises a scaffold 104 that is implanted in the tissue site 102 tofacilitate growth of the tissue at the tissue site 102. In this example,the tissue site 102 may have resulted from a defect or wound 106 in abone 107 of the patient's limb 103 which contains blood vesselsincluding blood vessel 108. The blood vessel 108 is fluidly coupled tothe scaffold 104 via a vessel-scaffold interface 110 to provide a supplyof blood to the scaffold 104. The reduced pressure therapy system 100further comprises a valve 112 to control the supply of blood from theblood vessel 108 to the scaffold 104 and a controller 114 electricallycoupled to the valve 112 which is varied between an open and closedposition by the controller 114. The blood pressure within the bloodvessel 108 forces the blood into the scaffold 104 and the tissue site102 when the valve 112 is opened. Growth and healing of the bone tissueat the wound 106 is enhanced by the various components of the bloodincluding, without limitation, clotting proteins, growth factors,albumin, and lymphocytes, that are supplied to the scaffold 104 and thetissue site 102 as the blood begins to flow through the valve 112.

The reduced pressure therapy system 100 may also comprise a reducedpressure source 116 for providing a reduced pressure to the scaffold 104to draw blood from the blood vessel 108 into the scaffold 104. Thereduced pressure source 116 is fluidly coupled to the scaffold 104 via aconduit 117 that is fluidly coupled to the scaffold 104 by aconduit-scaffold interface, or gradient inlet, 118. The conduit-scaffoldinterface 118 may be a manifold that distributes reduced pressure to thescaffold 104. The reduced pressure therapy system 100 further comprisesa canister 120 fluidly coupled between the conduit-scaffold interface118 and the reduced pressure source 116 to collect bodily fluids, suchas blood or exudate, that are drawn from the tissue site 102. Thus,besides drawing blood from the blood vessel 108 into the scaffold 104,the reduced pressure source 116 may also be used to provide reducedpressure therapy to the tissue site 102.

As used herein, the term “coupled” includes direct coupling or indirectcoupling via a separate object. The term “coupled” also encompasses twoor more components that are continuous with one another by virtue ofeach of the components being formed from the same piece of material.Also, the term “coupled” may include chemical, mechanical, thermal, orelectrical coupling. Fluid coupling means that fluid is in communicationbetween the designated parts or locations.

Upon opening the valve 112, blood flows into the scaffold 104 in variousdirections as indicated by the arrows 121. The controller 114 and thevalve 112 may be used to regulate the volume of blood being supplied tothe tissue site 102, such that the blood bathes all or a portion of thescaffold 104 as well as portions of the wound 106. However, the volumeof blood flowing through the valve 112 ultimately depends on the bloodpressure within the blood vessel 108. Consequently, when the valve 112is fully open and the blood pressure is too low, the reduced pressuresource 116 may be used to apply a reduced pressure to the scaffold 104to supplement the lower blood pressure. The magnitude and duration ofreduced pressure applied to the scaffold 104 by the reduced pressuresource 116 may be regulated to achieve the desired pressure and flowthrough the scaffold 104 in addition to any reduced pressure therapy. Insome embodiments, the scaffold 104 includes flow channels (not shown)that direct the blood to specific areas of the scaffold 104, such asthose areas where faster scaffold colonization is desired.

The valve 112 comprises a compression member 122 that pushes against theblood vessel 108 to close the blood vessel 108. It should be understoodthat the compression member 122 may be any type of closure mechanismknown to those skilled in the art. Additionally, the valve 112 may beoperable between the open and closed position using any type ofactuating stimuli, such as pressure (e.g., injecting air or a liquidinto the controller 114 through a conduit to close the valve), chemicalssuch as an oxygen generating reaction, osmotic stimulation, electricaldevice, an electrically controlled valve, or mechanical device. Thevalve 112 may include a port (not shown) through which the externalstimulus is applied. The valve 112 is operatively connected to thecontroller 114 via a valve control conduit 123 such as, for example, anelectrical conduit, mechanical conduit, or fluid conduit depending onthe type of valve utilized.

The reduced pressure therapy system 100 can be used to engineer tissueby providing blood from the blood vessel 108 to the scaffold 104. Growthand healing of the tissue at the wound 106 is enhanced by the variouscomponents of the blood including, without limitation, clotting proteinsand cells as described above, that are supplied to the scaffold 104 andthe tissue site 102 as the blood begins to flow through the valve 112.Upon implantation of the scaffold 104, proteins from the blood suppliedby the blood vessel 108 can cause a blood clot to form in the scaffold104 as an initial step in wound healing and tissue formation. Suchaccelerated clot formation can speed wound healing and tissue formation.In another example, blood is provided to the scaffold 104 later duringwound healing or tissue formation, to provide growth factors present inblood that encourage healing and tissue formation. Examples of growthfactors in blood include EGF, TGF-α, TGF-β, PDGF, aFGF, and bFGF. Thus,these growth factors are provided to the scaffold 104 with the blood.

Referring now to FIG. 2, another illustrative embodiment of the reducedpressure therapy system 100 is shown which comprises a blood supplyportion 124 that includes a blood vessel 108 that is fluidly coupled tothe scaffold 104 by a blood supply conduit 126 rather than beingconnected directly to the scaffold 104. The blood supply conduit 126 maybe a catheter or any other type of biocompatible tubing. The valve 112controls the flow of blood through the blood supply conduit 126 in thesame fashion as described above. Thus, the valve 112 varies between theopen and closed positions to control fluid communication between theblood vessel 108 and the scaffold 104. The blood supply portion 124allows blood to be indirectly supplied to the scaffold 104. In anotherembodiment, the blood supply conduit 126 is not connected to the bloodvessel 108, but rather to an external source of fluids that is locatedoutside of the patient's body (not shown).

The wound 106 may be an injury or defect, such as a fracture, located onor within any type of tissue site 102, including but not limited to,bone tissue, adipose tissue, muscle tissue, neural tissue, dermaltissue, vascular tissue, connective tissue, cartilage, tendons, orligaments. For example, the wound 106 can include burns, incisionalwounds, excisional wounds, ulcers, traumatic wounds, and chronic openwounds. Also, the bone 107 may be any type of bone, including longbones, short bones, flat bones, irregular bones, and sesamoid bones. Thewound 106 may also be any tissue that is not necessarily injured ordefected, but instead is an area in which it is desired to add orpromote growth of additional tissue, such as bone tissue. For example,reduced pressure tissue therapy may be used in certain tissue areas togrow additional tissue that may be harvested and transplanted to anothertissue location. The tissue site 102 may also include sites formaintenance of endogenous or exogenous grafts, and supportive scaffoldsfor subsequent implantation into a patient. The patient may be anymammal, such as a mouse, rat, rabbit, cat, dog, or primate, includinghumans.

In the context of this specification, the term “reduced pressure”generally refers to a pressure that is less than the ambient pressure ata tissue site that is subjected to treatment. In most cases, thisreduced pressure will be less than the atmospheric pressure of thelocation at which the patient is located. Although the terms “vacuum”and “negative pressure” may be used to describe the pressure applied tothe tissue site, the actual pressure applied to the tissue site may besignificantly greater than the pressure normally associated with acomplete vacuum. Consistent with this nomenclature, an increase inreduced pressure or vacuum pressure refers to a relative reduction ofabsolute pressure, while a decrease in reduced pressure or vacuumpressure refers to a relative increase of absolute pressure. Reducedpressure treatment typically applies reduced pressure at −5 mm Hg to−500 mm Hg, more usually −5 to −300 mm Hg, including but not limited to−50, −125, or −175 mm Hg.

The reduced pressure source 116 may be any device for supplying areduced pressure, such as a vacuum pump, wall suction, or other source.Also, the reduced pressure may vary in value per change in position toproduce three-dimensional reduced pressure gradients throughout thetissue site 102 and scaffold 104. A gradient is a rate of change of aphysical quantity that changes in value per change in position.Moreover, the conduit-scaffold interface 118 may be designed todistribute gradients for other physical characteristics, includingbiologic gradients, thermal gradients, electrical gradients, magneticgradients, chemical gradients, or positive pressure gradients, each ofwhich may be provided by a suitable gradient source.

Referring to FIG. 3, an alternative embodiment of the reduced pressuretherapy system 100 comprising a tissue therapy system 300 that utilizeselectrical charge in a modified scaffold 304 similar in structure to thescaffold 104 to facilitate the growth of tissue in the bone 107 of thepatient's limb 103. Reduced pressure may be applied to the modifiedscaffold 304 using the conduit-scaffold interface 118 as a manifold 318which is fluidly coupled to the reduced pressure source 116 via theconduit 117 as described above. The modified scaffold 304 comprises endsurfaces 328 disposed adjacent to the tissue site 102 and intramedullaryextensions 330 extending longitudinally therefrom into theintramedullary tissue 336 of the tissue site 102. The end surfaces 328are charged surfaces so that they draw electrolytic fluid from thetissue adjacent the intramedullary extensions 330 as a result of thestreaming potential induced thereon. The charged end surfaces 328 of themodified scaffold 304 may have a texture to enhance the deposition andgrowth of osteoblasts (Graziano et al., 2007) such as, for example, atexture of concave indentations or concave pits 332 which can be of anysize or shape. In some embodiments, the concave pits 332 are 10-120 μmin depth and 3-100 μm in depth.

The charged end surface 328 can be induced by any means known in theart. In some embodiments, the charged surface is induced by electricpolarization. See, for example, Nakamura et al., 2006, 2007, 2009; Itohet al., 2006. The polarization can establish a negative charge or apositive charge on the surface. In various embodiments, the chargedsurface is negatively charged. Charge also can be applied to the surfaceby surface treatment by, as an example, changing the surface chemistryto functionalize polymers, such as exposing a hydroxyl (—OH) group.

The tissue therapy system 300 can also cause fluid flow in the modifiedscaffold 304 without the use of reduced pressure. A streaming potentialcan be generated on the charged end surface 328 when an electrolyticfluid, such as blood or interstitial fluid from the tissue site 102,flows past the charged end surface 328. See, for example, Hillsley andFrangos, 1994. The charged end surface 328 can cause the tissue fluidsto flow along the charged end surface 328 due to the streaming potentialgenerated therein. A charged surface can induce electroosmotic flow,whereby cations in solution migrate to a charged end, osmoticallydragging fluid along with them.

Gradients other than reduced pressure gradients may also be applied tothe modified scaffold 304, including those described above. The gradientprovides additional flow at times when increased flow over thatgenerated by the streaming potential is desired, for example, whenremoval of excess fluid beyond that removed due to the streamingpotential is desired.

One example of a situation for which additional flow may be desired isany of the initial stages following implantation of the modifiedscaffold 304.

Using the tissue therapy system 300, a caretaker can apply the modifiedscaffold 304 to the tissue site 102, and induce a charge at the endsurfaces 328, such as by electric polarization. A streaming potentialmay be induced upon the charged end surface 328 when fluid from thetissue site 102 flows past the charged end surface 328, the streamingpotential draws electrolytic fluids comprising blood or interstitialfluids from the tissue site 102 adjacent the modified scaffold 304. Ifadditional fluid flow is desired through the modified scaffold 304, thecaretaker may also apply a reduced pressure to the modified scaffold 304using the manifold 318 and the reduced pressure source 116. Streamingpotential, electrolytes moving past a charged surface, also can inducebone formation. Concave surfaces of a charged material in a streamingpotential have been shown to form bone while convex surfaces absorb bone(Hillsley and Frangos, 1994).

As indicated above, the conduit-scaffold interface 118 may be a manifoldthat distributes reduced pressure to the scaffold 104 as shown morespecifically in FIG. 3 with reference to the manifold 318. The term“manifold” as used herein generally refers to a substance or structurethat is provided to assist in applying reduced pressure to, deliveringfluids to, or removing fluids from the tissue site 102. The manifold 318typically includes a plurality of flow channels or pathways thatdistribute fluids provided to and removed from the tissue site 102around the manifold 318. In one illustrative embodiment, the flowchannels or pathways are interconnected to improve distribution offluids provided or removed from the tissue site 102. The manifold 318may be a biocompatible material that is capable of being placed incontact with tissue site 102 and distributing reduced pressure to thetissue site 102. Examples of manifolds 318 may include, for example,without limitation, devices that have structural elements arranged toform flow channels, such as, for example, cellular foam, open-cell foam,porous tissue collections, liquids, gels, and foams that include, orcure to include, flow channels. The manifold 318 may be porous and maybe made from foam, gauze, felted mat, or any other material suited to aparticular biological application. In one embodiment, the manifold 318is a porous foam and includes a plurality of interconnected cells orpores that act as flow channels. The porous foam may be a polyurethane,open-cell, reticulated foam such as GranuFoam®, manufactured by KineticConcepts, Inc. of San Antonio, Tex. Other embodiments might include“closed cells.” These closed-cell portions of the manifold may contain aplurality of cells, the majority of which are not fluidly connected toadjacent cells. The closed cells may be selectively disposed in themanifold 318 to prevent transmission of fluids through perimetersurfaces of the manifold 318. In some situations, the manifold 318 mayalso be used to distribute fluids such as medications, antibacterials,growth factors, and various solutions to the wound 106 and theintramedullary tissue 336. Other layers may be included in or on themanifold 318, such as absorptive materials, wicking materials,hydrophobic materials, and hydrophilic materials.

The term “scaffold” as used herein refers to a substance or structureapplied to the tissue site 102 that provides a structural matrix for thegrowth of cells and/or the formation of tissue. The scaffold 104 may bea three-dimensional porous structure that may be infused with, coatedwith, or comprised of cells, growth factors, extracellular matrixcomponents, nutrients, integrins, or other substances to promote cellgrowth. The scaffold 104 can also take on characteristics of a manifoldby directing flow through the matrix. The scaffold 104 may have avariety of shapes including, for example, a substantially cylindricalshape as shown, a substantially circular shape (not shown, or arod-shape within the intermeddling tissue of the bone 107 (not shown).In some embodiments, the scaffold 104 is in the shape of a bone defectin the limb 103 of a patient.

Nonlimiting examples of suitable scaffold 104 materials includeextracellular matrix proteins such as fibrin, collagen or fibronectin,and synthetic or naturally occurring polymers, including bioabsorbableor non-bioabsorbable polymers, such as polylactic acid (PLA),polyglycolic acid (PGA), polylactide-co-glycolide (PLGA),polyvinylpyrrolidone, polycaprolactone, polycarbonates, polyfumarates,caprolactones, polyamides, polysaccharides (including alginates [e.g.,calcium alginate] and chitosan), hyaluronic acid, polyhydroxybutyrate,polyhydroxyvalerate, polydioxanone, polyorthoesthers, polyethyleneglycols, poloxamers, polyphosphazenes, polyanhydrides, polyamino acids,polyacetals, polycyanoacrylates, polyurethanes, polyacrylates,ethylene-vinyl acetate polymers and other acyl substituted celluloseacetates and derivatives thereof, polystyrenes, polyvinyl chloride,polyvinyl fluoride, polyvinylimidazole, chlorosulphonated polyolefins,polyethylene oxide, polyvinyl alcohol, Teflon®, hydrogels, gelatins, andnylon. The scaffold 104 can also comprise ceramics such ashydroxyapatite, coralline apatite, calcium phosphate, calcium sulfate,calcium carbonate or other carbonates, bioglass, allografts, autografts,xenografts, decellularized tissues, or composites of any of the above.In particular embodiments, the scaffold comprises collagen, polylacticacid (PLA), polyglycolic acid (PGA), polylactide-co-glycolide (PLGA), apolyurethane, a polysaccharide, a hydroxyapatite, or a polyethyleneglycol. Additionally, the scaffold 104 can comprise combinations of anytwo, three, or more materials, either in separate areas of the scaffold104, or combined noncovalently, or covalently combined (e.g., copolymerssuch as a polyethylene oxide-polypropylene glycol block copolymers, orterpolymers), or combinations thereof. Suitable matrix materials arediscussed in, for example, Ma and Elisseeff, 2005, and Saltzman, 2004.

In some embodiments, the scaffold 104 comprises a material that isosteoconductive (leads to bone deposition, provided that fullydifferentiated and competent osteogenic cells are available at the siteof implantation) or osteoinductive (induces de novo differentiation ofcompetent osteogenic cells from nonosteogenic and uncommitted cells).Examples of osteoconductive materials include hydroxyapatite, includinghydroxyapatite ceramics (Riminucci and Bianco, 2003).

The scaffold 104 can also comprise a living cell. The living cell can befrom any organism, including an Archaea, a prokaryote, or a eukaryote.In some embodiments, the cell is a mammalian cell. The cell can benaturally occurring or, alternatively, can be transformed to express arecombinant molecule, for example, a protein or nucleic acid (such as amiRNA). The term “cell” as used herein means any preparation of livingtissue (inclusive of primary tissue explants and preparations thereof),isolated cells, cell lines (including transformed cells), and hostcells. In some embodiments, autologous cells are employed. In otherembodiments, xenogeneic, allogenic, syngeneic cells, or stem cells areused.

These embodiments are not limited to the use of any particular cells.Included herein are any completely differentiated cells, partiallydifferentiated cells (e.g., adult stem cells), or undifferentiated cells(e.g., embryonic stem cells or induced pluripotent stem cells). In someembodiments, the cells are stem cells. These stem cells can be embryonicstem cells. Alternatively, the stem cells can be adult stem cells.Nonlimiting examples of adult stem cells are induced pluripotent stemcells (Takahashi and Yamanaka, 2006), mesenchymal stem cells,adipose-derived adult stem cells, hematopoietic stem cells, mammary stemcells, neural stem cells, endothelial stem cells, olfactory adult stemcells, tooth-derived stem cells, interfollicular stem cells, andtesticular stem cells.

The cells can also be, for example, osteoblasts, chondrocytes,fibroblastic cells (e.g., interstitial fibroblasts, tendon fibroblasts,dermal fibroblasts, ligament fibroblasts, cardiac fibroblasts,periodontal fibroblasts such as gingival fibroblasts, and craniofacialfibroblasts), myocyte precursor cells, cardiac myocytes, skeletalmyocytes, smooth muscle cells, striated muscle cells, satellite cells,chondrocytes (e.g., meniscal chondrocytes, articular chondrocytes,discus invertebralios chondrocytes), osteocytes, endothelial cells(e.g., aortic, capillary, and vein endothelial cells), epithelial cells(e.g., keratinocytes, adipocytes, hepatocytes), mesenchymal cells (e.g.,dermal fibroblasts, mesothelial cells, osteoblasts), adipocytes,neurons, glial cells, Schwann cells, astrocytes, podocytes, islet cells,enterocytes, odontoblasts, or ameloblasts. Different areas of thescaffold 104 can also comprise different cells. For example, thescaffold 104 may be seeded with osteoblasts over most of the scaffold104 and chondrocytes on a surface of the scaffold 104 where cartilage isdesired.

In some embodiments the scaffold 104 further comprises a bioactiveagent. A bioactive agent is a compound or element (e.g., iron) that canimprove the outcome of the treatment. Examples include nutritionalsupplements, antibiotics, small (<2000 mw) organic compounds (e.g.,serotonin, prostaglandin, prostacyclin, thromboxane, histamine),peptides (e.g., bradykinin), nucleic acids (e.g., aptamers or geneticvectors), and proteins, for example, a cytokine, an enzyme, or a proteincomprising an antibody binding site. Other nonlimiting examples ofpolypeptides that could be included in the scaffold 104 are virtuallyany hormone, neurotransmitter, growth factor, growth factor receptor,interferon, interleukin, chemokine, cytokine, colony stimulating factoror chemotactic factor protein, or polypeptide. Further examples includetranscription or elongation factors, cell cycle control proteins,kinases, phosphatases, DNA repair proteins, oncogenes, tumorsuppressors, angiogenic proteins, anti-angiogenic proteins, immuneresponse-stimulating proteins, cell surface receptors, accessorysignaling molecules, transport proteins, enzymes, anti-bacterial oranti-viral proteins or polypeptides, and the like, depending on theintended use of the ultimate composition. More specific examples includegrowth hormone (GH); parathyroid hormone (PTH, including PTH1-34); bonemorphogenetic proteins (BMPs) such as BMP-2A, BMP-2B, BMP-3, BMP-4,BMP-5, BMP-6, BMP-7, and BMP-8; transforming growth factor-α (TGF-α),TGF-β1, and TGF-β2; acidic fibroblast growth factor (aFGF); basicfibroblast growth factor (bFGF); granulocyte-colony stimulating factor(G-CSF); granulocyte/macrophage-colony stimulating factor (GM-CSF);epidermal growth factor (EGF); platelet derived growth factor (PDGF); aninsulin-like growth factor (IGF); leukemia inhibitory factor (LIF);vascular endothelial growth factor (VEGF); angiogenin; angiopoietin-1;del-1; follistatin; hepatocyte growth factor/scatter factor (HGF/SF); aninterleukin including interleukin-8 (IL-8); leptin; midkine; placentalgrowth factor; platelet-derived endothelial cell growth factor(PD-ECGF); platelet-derived growth factor-BB (PDGF-BB); pleiotrophin(PTN); progranulin; proliferin; tumor necrosis factor-α (TNF-α); nervegrowth factor (NGF); brain-derived neurotrophic factor (BDNF); Bcell-stimulating factor-3 (BSF-3); neurotrophin-3 (NT-3); neurotrophin-4(NT-4); glia maturation factor (GMF); ciliary neurotrophic factor(CNTF); glial cell-derived neurotrophic factor (GDNF); persephin;neurturin; artemin; growth differentiation factor-9 (GDF9); a matrixmetalloproteinase (MMP); angiopoietin 1 (ang1); ang2; and delta-likeligand 4 (DLL4). In some embodiments, the growth factor is growthhormone (GH), a bone morphogenetic protein (BMP), transforming growthfactor-α (TGF-α), a TGF-β, a fibroblast growth factor (FGF),granulocyte-colony stimulating factor (G-CSF),granulocyte/macrophage-colony stimulating factor (GM-CSF), epidermalgrowth factor (EGF), platelet derived growth factor (PDGF), insulin-likegrowth factor (IGF), vascular endothelial growth factor (VEGF),hepatocyte growth factor/scatter factor (HGF/SF), an interleukin, tumornecrosis factor-α (TNF-α), or nerve growth factor (NGF). The growthfactor can be derived from any species, including human.

As described above, the reduced-pressure therapy system 100 appliesreduced pressure to the wound 106 which may be distributed uniformlythrough the scaffold 104. In some embodiments, the scaffold distributesreduced pressure discontinuously through the scaffolds 104 and 304rather than being distributed in some uniform fashion thereby creating areduced pressure gradient. For example, the reduced pressure is notdelivered uniformly via a single point source, or via a plurality ofinlets along a linear flow passage, or through a substantiallyhomogeneous distribution manifold. In some embodiments, the reducedpressure gradient is discontinuous spatially, discontinuous inmagnitude, or discontinuous over time. Consequently, the reducedpressure gradients may occur throughout the wound 106.

A gradient is the rate of change of any variable physical quantity inaddition to reduced pressure including, without limitation, biologicgradients, thermal gradients, electrical gradients, magnetic gradients,chemical gradients, or positive pressure gradients. The conduit-scaffoldinterface 118 and manifold 318 as well as the scaffolds 104 and 304 maybe designed to distribute gradients for these other physicalcharacteristics. Referring to FIGS. 1 and 3, for example, theconduit-scaffold interface 118 and manifold 318 as well as the scaffolds104 and 304 may distribute reduced pressure gradients and/or biologicgradients as indicated by the arrows 121 and 321, respectively, asdescribed above in more detail and as further described in U.S.Provisional Patent Applications 61/142,053 and 61/142,065, which arehereby incorporated by reference. The circumferential scaffolds 104 and304 draw fluid radially from the intramedullary tissue 336 of the bone107 (not shown) through their respective flow channels as represented bythe arrows 121 and 321 in response to the reduced pressure or otherstimuli, but in a discontinuous fashion to create gradients to furtherpromote tissue growth and/or tissue healing. Thus, the methods andsystems of the present invention provide a means for active guidance oftissue regeneration through the implanted scaffolds 104 and 304 orwithin a compromised site, such as wound 106, to promote functionalrecovery utilizing these physical quantity gradients. As such, thesemethods and systems provide an active mechanism by which to promote theendogenous deposition of proteins and organization of the provisionalmatrix with biochemical and physical cues to direct cellularcolonization of the scaffolds 104 and 304 or tissue space within thewound 106.

REFERENCES

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All references cited in this specification are hereby incorporated byreference. The discussion of the references herein is intended merely tosummarize the assertions made by the authors and no admission is madethat any reference constitutes prior art. Applicants reserve the rightto challenge the accuracy and pertinence of the cited references.

In view of the above, it will be seen that the several advantages of theinvention are achieved and other advantages attained. As various changescould be made in the above methods and compositions without departingfrom the scope of the invention, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

We claim:
 1. A system for treating tissue at a tissue site in a mammal,the system comprising: a scaffold adapted to be disposed adjacent thetissue site and to be fluidly coupled to a blood vessel of the mammalfor receiving blood therefrom; and a valve adapted to be coupled to theblood vessel and controllable between an open position and a closedposition for regulating the flow of the blood from the blood vessel tothe scaffold; wherein the valve allows the blood to flow from the bloodvessel into the scaffold when in the open position and prevents theblood from flowing into the scaffold when in the closed position.
 2. Thesystem of claim 1, further comprising a catheter adapted to fluidlycouple the blood vessel to the scaffold.
 3. The system of claim 2,wherein the valve is coupled to the blood vessel indirectly by beingcoupled to the catheter.
 4. The system of claim 1, wherein the systemfurther comprises a gradient inlet that provides a gradient to thescaffold.
 5. The system of claim 4, wherein the gradient inlet is areduced pressure inlet.
 6. The system of claim 1, wherein the valveopens or closes in response to an external stimulus.
 7. The system ofclaim 6, wherein the external stimulus is at least one of pressure,electrical, mechanical, and chemical stimulation.
 8. The system of claim6, further comprising a port for applying the external stimulus.
 9. Thesystem of claim 8, wherein the external stimulus is positive pressure.10. The system of claim 1, further comprising a reduced pressure systemfluidly coupled to the scaffold for providing a reduced pressure to thescaffold.